Lets do a little experiment.
Post your level, your grimoire score, and how many legendary items and/or engrams you've gotten.
I have a feeling the higher the grimoire the more legendary drops you get.
I'm 1355, Level 24 and I've only ever gotten ONE legendary engram. Haven't seen anything purple before or after
Level 25 Titan.
I own 2 legendaries. A Chest I bought from Dead Orbit, and a Machine Gun (Void) I got as a gift from Rank 4 Cryptarch.
I've decoded 10 Purple Engrams.
-Blue Helmet
-Blue Chest
-Purple Warlock Boots
-2 Strange Coins
-2 Motes of Light
-Purple Warlock Boots again
-Blue Fusion Rifle
-Blue Helmet
-Blue Chest
-Purple Chest Piece with identical stats to my own, but different ammo upgrades.
I also just hit rank 3 with Dead Orbit, and they gave me the exact same Legendary machine gun I already had.
Meanwhile, 2 of my friends have gotten exotic bounties, and I'm the only one still level 25. They're all 26-27.
Grimoire rank is 1530. I've been playing about 4 hours on weekdays and 14-16 hours on weekends.